Or in your site front page, in the admin bar find Edit Page ( Back-end Editor ) or Edit with WPBakery Page Builder ( Front-end Editor )
For changing size and margin, go to Theme Options > Header > Header > Logo element
And for changing margins go to Theme Options > Header > Header > Social Element
For disabling slider or changing it with other title type
Example Breadcrumbs or Title, Go to Page Edit > Page Settings > Header Settings > Title Type
For overall website page title type go to Theme Options > Header > Title & Bredcrumbs
Instead Quick Contact also you can create any page and assign it.
In widgets find Footer 1 to Footer 4 sidebar area sections and edit them.
For changing background color of Footer, Go to Theme Options > Footer > Footer Widgets > Row Container Style Kit
For changing Background image, hover over content box and edit it to find Overall style kit. Also box have padding top, you can also change it for your need.
For editing menu navigation settings go to Theme Options > Header > Header > Menu Element
And for styling menus go to Theme Options > Header > Header > Menu Styles of this Row